The optical recording media can be classified into two types; one is designed to form physically deformed portions (pits) including holes and concavities on parts of a recording layer, and the other is designed to generate phase changings on parts of the recording layer and form portions where optical properties (refractive index, reflectance, transmission and others) are changed. The optical recording media in the type of forming physically deformed portions such as holes on parts of the recording layer (pit-forming type) are mainly used at present.
The pit-forming type optical recording media, however, have such problems as 1 a relatively large optical power for recording is required when forming pits on parts of the recording layer, 2 the shape of recording pits is hard to 3 recording at high density is difficult, and 4 two optical recording media cannot be adhered closely and laminated to each other. To the contrary, the optical recording media designed to change optical properties due to phase change on parts of the recording layer (phase-changing type) can solve the above problems associated with the pit-forming type optical recording media.
As phase-changing type optical recording media, for example, optical recording media having alloyed recording layers composed of Te, Ge and Sb (Japanese Patent L-O-P Publns. No. 62-19618) and having a recording layer composed of Te, Sn, Zn and S (Japanese Patent L-O-P Publns. No. 62-167632) are well known. In such optical recording media having recording layers composed of alloy, however, it is relatively difficult to control the composition of alloy when forming the recording layer on the substrate, which causes low reproducibility, and it is impossible to produce the optical recording media having a desired constant performance at high productivity.
A phase-changing type optical recording media, having a recording layer containing Te Ox (Japanese Patent L-O-P Publns. No. 50-46317) is also known. This optical recording media include such problems that 1 stability in amorphous state is low, that is, its service life is short because the crystallization temperature of the recording layer is low, and 2 the safety in the process of forming the layer cannot be guaranteed when the reactive sputtering is executed in the atmosphere of oxygen because oxygen accerates burning.
The present inventors made an extensive effort on the optical recording media having a recording layer of the phase-changing type containing Te as its main ingredient to find the fact that a optical recording media having a recording layer containing N and, if necessary, Pd in addition to Te between a substrate and a protective layer has improved amorphous stability (a property keeping the amorphous state stable) of the recording layer and enhanced oxidation resistance, and that the life of the optical recording media can be prolonged. The present inventors have also found that by setting the thickness of the recording layer in a specific range, readout error of the information can be reduced.